1. Field of the Invention
The present invention relates to a retaining mechanism for gears of a constantly meshing gear transmission, wherein the retaining mechanism prevents gears from slipping while restricting operational force for speed changing.
2. Background Art
A conventional constantly meshing gear transmission is constructed as follows. A rotary shaft to be variably rotated is provided thereon with a plurality of relatively rotatable transmission gears and at least one fixed hub. The hub is disposed between two adjacent gears and formed on the outer peripheral surface thereof with a male spline. Each of the adjacent gears forms a boss on a side thereof facing the hub. A male spline is formed on the outer peripheral surface of the boss. A clutch slider is axially slidably fitted on the hub so that a female spline provided on the inner periphery of the clutch slider constantly meshes with the male spline of the hub.
A fork is connected to the clutch slider and fixed to a fork shaft. By manipulating a shift lever for shifting (speed changing), the fork shaft moves axially together with the clutch slider so that the female spline of the clutch slider selectively meshes with the male spline of one of the adjacent gears with the hub therebetween so as to fix the selected gear to the rotary shaft through the hub, thereby rotating the rotary shaft at the speed corresponding to the selected gear.
In such a construction, a detent mechanism for holding the clutch slider in place while allowing the clutch slider to slide thereacross is provided on the fork shaft or any member interlocking with the fork shaft. However, the clutch slider engaging with the gear through the splines sometimes slips from the gear naturally. This phenomenon results in unexpected shifting (change to a different speed or to neutral). To avoid the phenomenon, a spring of the detent mechanism may be strengthened so as to increase the force for retaining the clutch slider. The increased force of the detent mechanism is advantageous in retaining the clutch slider; however, the shift lever becomes too heavy to be manipulated for intentionally sliding the clutch slider across the detent mechanism.
An object of the present invention is to provide a gear retaining mechanism for a constantly meshing gear transmission wherein a clutch slider is retained in place steadily without increasing the force of the detent mechanism for retaining the clutch slider. The constantly meshing gear transmission comprises a rotary shaft, a hub fixed on the rotary shaft, the hub being provided on an outer periphery thereof with a male spline, a clutch slider axially slidably fitted on the hub, the clutch slider being provided on an inner periphery thereof with a female spline constantly meshing with the male spline of the hub, and a gear relatively rotatably provided on the rotary shaft, the gear being provided on an outer periphery thereof with a male spline enabled to mesh with the female spline of the clutch slider. The clutch slider is slid along the rotary shaft for fixing the gear to the rotary shaft through the hub so that the female spline, while meshing with the male spline of the hub, meshes with the male spline of the gear.
To achieve the object, according to the present invention, each of the male splines of the hub and the gear has an axially tapered portion. Preferably, the tapered portion of the male spline of the hub is narrowed axially oppositely to the tapered portion of the male spline of the gear. When the female spline, while meshing with the male spline of the hub, meshes with the male spline of the gear, the female spline abuts at opposite axial ends thereof against the tapered portion of the male spline of the gear and the tapered portion of the male spline of the hub so as to retain the clutch slider.
The gear is rotated by a prime mover so as to press the tapered portion of the male spline of the gear against the female spline of the clutch slider, thereby forcing the female spline in one axial direction. On the other hand, the hub fixed on the rotary shaft, to which ground load applied on a grounding wheel of a vehicle is transmitted, tends to resist the rotation of the clutch slider engaging with the gear so as to press the taper portion of the male spline of the gear against the female spline of the clutch slider, thereby forcing the female spline of the clutch slider in axially opposite direction.
Consequently, while the vehicle travels in the setting speed of the gear, the female spline is forced in axially opposite directions. In other words, each end of the female spline is difficult to move toward the wider end of the corresponding tapered portion abutting against it because great force is required to move the female spline in such a way. The great force is equal to the normal operation force for shifting the clutch slider and is greater than a force naturally applied on the normally sliding clutch slider, which is a differential force generated between the upstream and downstream portions of the rotary shaft.
Usually, a plurality of gears serve as the gear. Whichever gear of the plurality of gears may be selected to be fixed to the rotary shaft by the clutch slider through the hub, the female spline, while meshing with the male spline of the hub, meshes with the male spline of the selected gear so that the female spline abuts at opposite axial ends thereof against the tapered portion of the male spline of the selected gear and the tapered portion of the male spline of the hub, thereby stably retaining the clutch slider.
Suppose that a pair of first and second gears serving as the plurality of gears are disposed on one side of the hub so that the male spline of the first gear is disposed between the male spline of the second gear and the male spline of the hub. To correspond to such arranged first and second gears, the female spline of the clutch slider is provided at opposite ends thereof with a first tooth and a second tooth. When the clutch slider meshes with the second gear and the hub so as to select the second gear to be fixed to the rotary shaft, the male spline of the second gear meshes with the first tooth, and the male spline of the hub meshes with the second tooth. At this time, the male spline of the first gear is allowed to pass through a gap in the female spline of the clutch slider between the first tooth and the second tooth. Thus, a single clutch slider may be used for selecting one of the first and second gears disposed on one side of the hub, thereby reducing the number of parts, costs, and the size of the transmission.
When the clutch slider meshes with the first gear and the hub so as to select the first gear to be fixed to the rotary shaft, the tapered portion of the male spline of the first gear abutting against the first tooth is narrowed axially oppositely to the tapered portion of the male spline of the hub abutting against the second tooth, and when the clutch slider meshes with the second gear and the hub so as to select the second gear to be fixed to the rotary shaft, the tapered portion of the male spline of the second gear abutting against the first tooth is narrowed axially oppositely to the tapered portion of the male spline of the hub abutting against the second tooth. Thus, whichever gear of the first and second gears may mesh with the clutch slider, the clutch slider is securely retained in place.
Correspondingly, the male spline of the hub may include a pair of first and second tapered portions. The second tooth of the female spline of the clutch slider abuts against the first tapered portion when the first tooth of the female spline of the clutch slider abuts against the tapered portion of the male spline of the first gear. The second tooth of the female spline of the clutch slider abuts against the second tapered portion when the first tooth of the female spline of the clutch slider abuts against the tapered portion of the male spline of the second gear.
If the tapered portions of the respective first and second gears are narrowed axially oppositely to each other, the first tapered portion is narrowed axially oppositely to the second tapered portion in the female spline of the clutch slider.
If the vehicle equipped with the transmission is provided with a parking brake, the clutch slider may be enabled to mesh with the first gear, the second gear, and the hub together so as to fix both the first gear and the second gear to the rotary shaft, thereby corresponding to the actuation of the parking brake.
A third gear, which is provided on an outer periphery thereof with a male spline to mesh with the female spline of the clutch slider, may be relatively rotatably provided on the rotary shaft so that the male spline of the hub is disposed between the male spline of the first gear and the male spline of the third gear. The first and second gears may have different rotary speeds in the same rotational direction, and the third gear may be rotated oppositely to the first and second gears. Such three gears are enabled to be selectively fixed to the rotary shaft through the hub by a single clutch slider, thereby reducing the number of parts, costs, and the size of the transmission.
For securely retaining the clutch slider meshing with the third gear, the third gear may also serve as one of the plurality of gears including the male spline having the tapered portion. When the clutch slider meshes with the third gear and the hub so as to select the third gear to be fixed to the rotary shaft, the second tooth abuts against the tapered portion of the male spline of the third gear, and the first tooth abuts against the tapered portion of the male spline of the hub. Furthermore, the tapered portion of the male spline of the third gear abutting against the second tooth may be narrowed axially oppositely to the tapered portion of the male spline of the hub abutting against the first tooth.
These, other and further objects, features and advantages will appear more fully from the following description.